Cannot find in the NEC where it defines at what distance (conductor length) from the transformer an OCPD be located and still qualify as protecting the transformer secondary. For example: a single phase 480-120/240VAC transformer feeding a panelboard with main breaker. Will this panel main breaker qualify as transformer secondary protection if the transformer secondary conductors are 5ft. long? What about 6, 7, or 8ft.? Appreciate any help.
Transformer Secondary Protection Location
- Thread starter bozo
- Start date
- Status
electricalperson
Senior Member
- Location
- massachusetts
correct me if im wrong but i believe secondary conductors are not required to have protection as long as the primary conductors are protected..i dont have a code book handy right now
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Take a look at 240.21(C). Protection on the primary side only is discussed in sub-article (1). Most of the applications I encounter come under sub-article (2) - max 10 feet.
charlie b said:
Appreciate the reply. My question concerns transformer secondary protection as defined in Art. 450 as opposed to secondary conductor protection. In table 450.3(B) you are given allowable max protection limits for primary only protection and primary/secondary protection. My question concerns the allowable max distance between transformer secondary and OCPD to qualify the OCPD as transformer secondary protection. Presume there would be some distance limits. Hope I stated my question clearly.
- Location
- Illinois
- Occupation
- retired electrician
Mike
There is no distance limit for the location of the transformer secondary OCPD. That being said, you have to connect conductors to the transformer secondary and when you do there are limits on the location of the conductor OCPD in 240.21(C).
Don
There is no distance limit for the location of the transformer secondary OCPD. That being said, you have to connect conductors to the transformer secondary and when you do there are limits on the location of the conductor OCPD in 240.21(C).
Don
Transformer Secondary Disconnect, Interior Distribution
Transformer Secondary Disconnect, Interior Distribution
While not having my code book handy, back in the 80s I recall a rule that required a disconnect within 50 feet of the secondary of a transformer. Its a design practice I maintain, as it makes sense to have the ability to disconnect power on either side of a dry type transformer within a convenient distance of the transformer. Makes swapping out transformers easier if nothing else.
On the rule, I also recall the Durham NC Chief Elect Inspector (and then code panelist) carefully explain the rule was wire length and not horizontal length. As he stridently made us move the switches closer to the transformer on a fairly large exec center.
While the code does discuss primary protection where no secondary protection is used/required, secondary overcurrent protection is typically used We require it in all of our projects.
Transformer Secondary Disconnect, Interior Distribution
While not having my code book handy, back in the 80s I recall a rule that required a disconnect within 50 feet of the secondary of a transformer. Its a design practice I maintain, as it makes sense to have the ability to disconnect power on either side of a dry type transformer within a convenient distance of the transformer. Makes swapping out transformers easier if nothing else.
On the rule, I also recall the Durham NC Chief Elect Inspector (and then code panelist) carefully explain the rule was wire length and not horizontal length. As he stridently made us move the switches closer to the transformer on a fairly large exec center.
While the code does discuss primary protection where no secondary protection is used/required, secondary overcurrent protection is typically used We require it in all of our projects.
- Status